Many can bodies for food, beverages or other products are provided with easy open can ends that are characterized by having a pull tab attached to the can end which is used to fracture a tear panel on the can end defined by a score line on the can end. The pull tab may be lifted to depress the tear panel in order to provide an opening in the can end for dispensing the contents of the container.
Likewise, many food products are sold in can bodies provided with full open easy open can ends that are characterized by having a pull tab attached to the can end which is used to fracture a score line that circumscribes the circumference of the end panel to define an opening panel. The pull tab may be lifted to fracture the score line. After the score line is fractured, the pull tab may be pulled upward from the container which severs the remainder of the score line in order to remove the entire opening panel for dispensing the contents of the container.
In the manufacture of an easy open can end, a shell is conveyed to a conversion press. In the industry, a pre-converted can end is commonly referred to as a shell. In the typical operation of a conversion press, a shell is introduced between an upper tool member and a lower tool member, which are in the open, spaced apart position. A press ram advances the upper tool member toward the lower tool member in order to perform any of a variety of tooling operations such as rivet forming, paneling, scoring, embossing, and final staking. After performing a tooling operation, the press ram retracts until the upper tool member and lower tool member are once again in the open, spaced apart position. The partially converted shell is transported to the next successive tooling operation until an easy open can end is completely formed and discharged from the press. As one shell leaves a given tooling operation, another shell is introduced to the vacated operation, thus continuously repeating the entire easy open can end manufacturing process. Examples of easy open can ends can be found in U.S. Pat. Nos. 4,465,204 and 4,530,631. Conversion presses can operate at speeds that manufacture in excess of 500 can ends per minute per lane, with certain presses having four lanes of tooling manufacturing in excess of 2000 converted can ends per minute.
It has been the practice in the industry to continue to strive to reduce the starting gauge of the metal sheet stock used to form the can end. The current practice is to use metal with a starting gauge of approximately 0.008 inch (0.20 mm). As such, tooling stations in a conversion press must be rigorously maintained within prescribed operating tolerances due to the thin sheet stock used in the press. In the production of a converted can end in a conversion press, the scoring station is of particular concern. The scoring station employs a tooling member that has a knife edge which defines the tear panel or opening panel on the public side of the can end.
Steel sheet stock used in the manufacture of can ends has a coating which protects the metal by inhibiting oxidation, corrosion or rust from forming on the surface of the metal. During the conversion process, damage to the protective coating typically occurs while forming the score that defines the tear panel or opening panel of the can end. As noted above, in the conversion of a shell into a can end with openable features thereon, a score line is formed. This score line defines the tear panel or opening panel described above. The score line is the most likely location where damage is caused to the pre-conversion, protective coating. Any oxidation, corrosion or rust on the surface of the can end represents an unattractive product appearance to the consumer and is unacceptable to canmakers in general.
In the industry, as a precautionary measure to prevent oxidation, corrosion or rust from appearing on the can end, many canmakers apply a fluid, repair fluid, lacquer or paint to the scored area of the can end by spraying the can end. The accepted spraying apparatus and method in the industry for score repair on full open easy open ends utilizes high pressure spray atomization which forms small droplets or particles of fluid, repair fluid, lacquer or paint from the fluid, repair fluid, lacquer or paint. Atomization can be achieved by high pressure impingement (between 100 psi (0.690 MPa) to 600 psi (4.137 MPa)) on an orifice of a spray head or using a secondary low pressure air source (around 100 psi (0.690 MPa)) to break the fluid into small controlled droplets or particles. The problem with the atomization method is that it generates overspray which is detrimental to the efficiencies of the machine due to the extensive cleaning required on the surrounding transfer mechanism or belt of the machine. Overspray is defined herein as the additional fluid, repair fluid, lacquer or paint that does not transfer directly to the can end and sprays beyond the scored surface of the can end onto the transfer mechanism, belt or machine. The two part epoxy coating mixtures commonly used as a fluid is difficult to manage on a continuously operating machine when overspray occurs because the fluid, repair fluid, lacquer or paint builds up on the surrounding transfer mechanism of the machine, and requires routine cleaning and maintenance to keep the machine running efficiently.
The present invention implements a low pressure solid stream spray head and method, which significantly reduces spray beyond the scored surface of the can end and allows for greater machine efficiencies due to reduced downtime associated with routine cleaning and maintenance. The solid stream nozzle provides prolonged stream integrity, which results in delayed breakup and drop formation after leaving the nozzle orifice. The fluid is essentially extruded in a continuous stream as opposed to a pattern of droplets or particles.
In certain humid environments where oxidation and corrosion are of greater concern than in less humid environments, many canmakers apply more fluid, repair fluid, lacquer or paint to the can end to prevent rust from appearing on the can end. The present low pressure non-atomization or solid stream spray head and method allows for a low and high film weight (up to 20 mg or more) to be applied on the can end without the heavy overspray associated with prior art high pressure atomized or droplet spray head repair systems. The industry accepted high pressure atomization or droplet spray head applies a lower film weight (around 10 mg) on a can end by providing a very thin layer of fluid, repair fluid, lacquer or paint coating at high pressure. Even at this reduced film weight, the industry accepted atomization spray head presents overspray problems. Also, the prior art atomized spray head does not apply enough film weight to the can ends in certain environments and contaminates the transfer mechanism, belt or machine because of overspray.
There continues to be a need in the art for a spray apparatus and method for the repair of can ends that can apply low and high film weights to the can ends than was previously known in the art. Additionally, there continues to be a need in the art for a spray apparatus and method that does not generate a high volume of overspray or substantially avoids overspray.